Dissociations between impairments in microlinguistic and macrolinguistic abilities were examined in brain-damaged patients to assess whether these abilities are psychologically and neurologically distinct. The discourse productions of three groups of patients with equally severe fluent language disorders, but varying neuropathology and varying profiles of associated nonlinguistic cognitive impairments, were analyzed. Patients with fluent aphasia secondary to a single left-hemisphere CVA showed the greatest impairment on syntactic and lexical error measures taken to reflect microlinguistic abilities, but normal performance on measures of macrolinguistic organization (i.e., thematic coherence). Patients with probable Alzheimer's Disease were impaired on thematic coherence measures, but not on measures reflecting microlinguistic syntactic and phonological processes. Closed head injury patients whose primary clinical symptom was a fluent language disorder were impaired on both microlinguistic and macrolinguistic measures, which appears to parallel their deficits both in language-specific and in nonspecific, higher-order, diffusely organized cognitive processes.